Gas springs are typically utilized to yieldingly resist movement of a body such as a clamping ring for a metal blank in a die in a press for forming sheet metal parts. These springs are generally constructed with an actuating rod connected to a piston or head slidably received in a cylinder having a chamber that is charged through a filler valve in the cylinder to a predetermined pressure, such as 2000 PSI, with an inert gas, such as nitrogen. This provides a gas spring or cushion permitting the rod to yieldably move toward its retracted position when a force, applied externally to the rod, exceeds the opposing force produced by the gas in the chamber acting on the head.
To charge the chamber with gas for a gas spring in a system piped to a remote control panel, a gas supply line is connected to the cylinder through a hose with a nipple or fitting threadably received in a valve cavity in the cylinder which contains the filler valve and communicates with a passage leading to the cylinder chamber. Pressurized gas is introduced into the chamber through the filler valve until the pressure of the gas within the chamber typically reaches the line pressure. The filler valve has a poppet valve body with a core valve which permits only one-way flow of gas during filling of the chamber. The poppet valve body is movable within the cavity between a first sealed position to prevent removal of gas from the chamber and a second position for bleeding gas from the chamber to relieve pressure within the chamber.
The poppet valve body has a first effective area in communication with the gas supply line and a generally opposed second effective area in communication with the passage leading to the cylinder chamber. To enable the gas within the chamber to be compressed to a substantially greater pressure than the pressure of the gas in the supply line, the first effective area is larger than the second effective area. The maximum pressure to which gas within the chamber can be compressed is typically dependent upon the ratio of these effective areas. A gas spring having a filler valve of this construction is disclosed in U.S. Pat. No. 4,838,527.
Although filler valves of this construction have been disclosed to have an effective area ratio in the range of about 4:3 to 4:1, they have been practically limited due to the contruction of a seal on the body between the valve body and cylinder when in the sealed position to a maximum ratio of about 3:1 which limits the maximum pressure to which the gas can be compressed in the chamber during operation before the valve body moves to bleed gas from the chamber. As a result, the use of filler valves of this construction requires a larger chamber volume, a piston with a larger effective area and/or a longer rod and chamber to provide a longer stroke to avoid exceeding this maximum pressure during operation resulting in a larger, less compact gas spring construction. Furthermore, these valves are received in the valve cavity in the cylinder and retained within the cavity by the nipple making them more difficult, time consuming and expensive to service, repair and replace.